The present invention relates to an ultrasonic motor used for a clock, an automatic focusing system of a camera, an opening and closing operation of a shutter and a drive operation of an X-Y stage, and more particularly to an improvement of an ultrasonic motor and an electronic apparatus with an ultrasonic motor which reduces an abrasion in a pressure-contact portion between a pressing member and a pivot member.
In recent days, an attention has been given to an ultrasonic motor which generates an oscillating wave in an oscillator connected to a piezoelectric element and which can move a moving body by applying a frictional force due to the oscillator (for example, refer to Japanese Patent Examined Publication No. 62-92781).
Further, an ultrasonic motor of a rotating type is provided with an oscillator fixed to a central shaft, a piezoelectric element connected to a lower surface of the oscillator, a rotor brought into contact with a projection provided in the oscillator, a pivot fixed to a rotating center of the rotor, and a pressing spring for pressing the pivot (for example, refer to Japanese Patent Unexamined Publication No. 8-107686).
In accordance with this structure, the pressing spring urges the pivot so as to apply a pressing force to the rotor and the oscillator, generates a suitable frictional force to the rotor and the projection in the oscillator, and rotates the rotor in a predetermined direction.
However, since the pressing spring and the pivot are made of the same kind of material, both are hard cohered and abraded. Further, even when a lubricating oil is supplied between the pivot and the pressing spring, the lubricating oil is lost after the rotor rotates for a long time rotation, so that the pivot and the pressing spring are abraded.
As a result abrasion of the pivot or the pressing spring is associated with the problems of changing the pressing force and the frictional force, lowering a rotating speed of the rotor and a torque of the motor, and further stopping the motor.
Further, since the pivot is always pressure-contact at the same point with the pressing spring, there is a problem that a load of the pivot against the frictional force generated in the pressure-contact portion is great, so that the pivot is highly abraded.